In recent years, with higher integration of semiconductor devices, fine patterns exceeding the transfer limit of the photolithography technique have been required in the semiconductor industry. In view of this, the EUV lithography being an exposure technique using extreme ultraviolet (Extreme Ultra Violet: hereinafter referred to as EUV) light with a shorter wavelength is expected to be promising. Herein, the EUV light represents light in a wavelength band of the soft X-ray region or the vacuum ultraviolet region and, specifically, light having a wavelength of about 0.2 to 100 nm. As a mask for use in the EUV lithography, there is proposed an exposure reflective mask, for example, described in Patent Document 1 noted below.
This reflective mask has a multilayer reflective film formed on a substrate and adapted to reflect exposure light, a buffer film formed in a pattern on the multilayer reflective film, and further an absorber film formed in a pattern on the buffer film and adapted to absorb the exposure light. The buffer film is provided between the multilayer reflective film and the absorber film for the purpose of protecting the multilayer reflective film in pattern forming and correcting processes of the absorber film. The light incident on the reflective mask mounted in an exposure apparatus (pattern transfer apparatus) is absorbed at a portion where the absorber film is present, but is reflected by the multilayer reflective film at a portion where the absorber film is not present so that an optical image is transferred onto a semiconductor substrate through a reflective optical system.
Such a reflective mask is manufactured, for example, through the following processes.
(1) A predetermined resist pattern is formed on an upper surface of a reflective mask blank in which the multilayer reflective film, the buffer film, and the absorber film are formed in this order on the substrate and, using the resist pattern as an etching mask, a predetermined pattern is formed in the absorber film by dry etching.
(2) Herein, using inspection light, an inspection is performed to check whether or not the pattern is formed as designed in the absorber film. In this event, the inspection is carried out by detecting inspection light reflected by the absorber film and inspection light reflected by the buffer film which is exposed by the removal of the absorber film, thereby observing the contrast therebetween.
(3) If, as a result of the inspection, it is found out that the pattern of the absorber film has a white or black defect, correction of a pinhole or the like is carried out by FIB-assisted deposition or the like for the white defect, while, correction is carried out by removing an unnecessary portion by FIB irradiation or the like for the black defect portion.
(4) Then, using as an etching mask the absorber film formed with the above-mentioned pattern, the buffer film is removed by dry etching according to the absorber film pattern, thereby transferring the pattern to the buffer film.
(5) Finally, using inspection light, a final confirmation inspection of the formed pattern is performed. In this event, the inspection is carried out by detecting inspection light reflected by the absorber film and inspection light reflected by the multilayer reflective film which is exposed by the removal of the absorber film and the buffer film, thereby observing the contrast therebetween.